Neutron detection depends on the analysis of energetic products formed by interactions between sensitizer nuclei and incident neutrons. Fast neutrons are normally detected using actinide sensitizers coated inside fission chambers and hydrogen to measure the elastic scattering of protons. For slow neutrons, other materials are attractive, for example 3He or BF3 in gas filled tubes, 6Li-loaded glass, boron or lithium lined gas chambers, and organic and inorganic scintillators. Thermal neutron detection typically requires the conversion of target nuclei into a detectable particle. The most used reaction is that of the direct conversion by reaction with a neutron of 10B to 7Li and alpha particles. Among the organic scintillators boron-loading is the most common method of sensitization and this is usually accomplished by dissolution of an organic boron compound into a polyvinyltoluene matrix.
In the early 1990's silicones were first investigated as a replacement for polyvinyltoluene in scintillators as silicones are also very robust in high radiation fields, and exposure of up to 10 megarads can be tolerated. Unlike polyvinyltoluene, yellowing does not occur after absorbing megarad doses of neutrons. As silicones are elastomer rather than a plastic, no crazing and cracking due to residual stresses will occur. Another attractive features of silicones for scintillators is that the rubber can be cast in any shape or form and are typically heat resistant to 200° C.
Carboranes have been dissolved into silicone rubber to produce centimeter-thick disks that were clear and were examined as thermal neutron detectors. Carboranes is a cluster composed of boron and carbon atoms. Like many of the related boranes, these clusters are polyhedra. Carboranes have the chemical formula C2B10H12 and exist in three isomeric forms. As each molecule contains ten boron atoms their use as scintillation targets is desirable. Unfortunately, the solubility of the carboranes in silicone is significantly limited and the volatility of the carboranes results in sublimation of the carboranes from the silicone rubber, which ultimately rendering the rubber insensitive to thermal neutrons.
The incorporation of a carborane in a silicone polymer backbone is disclosed in Keller et al. U.S. Pat. No. 5,969,072 for use as ceramic or thermostet polymeric precursors. These carborane containing silicone polymers have been shown to have good thermo-oxidative stability.